Alert
On Saturday, August 3, 2019 two aircraft came closer to each other than dictated by the minimum separation standard. The aircraft departed one after the other from runway 18R/36L (Polderbaan) at Schiphol Airport. LVNL (Air Traffic Control the Netherlands) is conducting the investigation into this occurrence itself and has reported it to the Onderzoeksraad voor Veiligheid (Dutch Safety Board).
Description of occurrence
An aircraft of the type Airbus A340-300 (A343) took off from runway 36L (Polderbaan). After that, an aircraft of the type Airbus A330-300 (A333) took off. Both aircraft initially flew the same route after taking off. The A333 which took off second was flying faster than the A343, so it started catching up to the first aircraft. The difference in speed between the aircraft increased from 15 knots (28 kmph) to 45 knots (83 kmph).
Both aircraft are placed in the ‘heavy’ wake turbulence category. This means that the distance between the two aircraft must be 4 nautical miles (7.4 kilometers) horizontally or 1000 feet (300 meters) vertically. The minimum separation measured between the A343 and the A333 was 2.4 nautical miles (4.4 kilometers) horizontally. At that time, each of the aircraft flew in a different direction. There was no danger of collision.
Results of the investigation
The main cause of the occurrence was the fact that the A333 had a substantially faster rate of climb than the A343. As a result, the A333 flew closer behind the A343 than it intended. After taking off from runway 36L (Polderbaan), the pilot of the A343 contacted the radar controller. The radar controller instructed the A343 to climb to Flight Level 130 (above 4 kilometers). The A333 that took off behind it started with a slightly higher rate of climb than the aircraft before it. The radar controller then noticed that the difference in speed was increasing. At that time, the A333 was not yet on the radio frequency for this radar controller; it was still on the frequency of the air traffic control tower. The radar controller contacted the tower controller about this. At that time, the pilot of the A333 hailed the radio frequency of the radar controller. Since the A343 in front was flying a different route than the A333, no further intervention took place.
Follow-up action based on this investigation
The internal LVNL Safety Magazine will include an article on speed differences immediately after take-off. This occurrence will be used as an example in that article.